Magnetic disk units mounted on computers and the like as an information recording apparatus are required to have higher recording densities so as to store vast amounts of information without increasing the size of the apparatus. In order to increase the recording density of magnetic disks, a high-coercivity recording medium is used to meet the need for reliably writing minute pieces of recording information in the recording medium. To record the high-coercivity recording medium, it is necessary to focus a strong recording field in a very small region. However, as the recording density is increased, it becomes technically difficult to focus the strong recording field in the very small region.
As a technology to overcome this problem, energy assisted recording technology that assists recording by adding separate energy to the recording field is regarded as a likely candidate. As the energy used for the assisting, heat and high frequency magnetic field are currently considered more practically promising.
The energy assisted recording using heat is referred to as “thermally assisted magnetic recording” or “optically assisted recording”. At the time of recording, the recording medium (ferromagnetic material) is irradiated with light simultaneously with magnetic field application, thus heating the medium to temperatures near the Curie temperature of the recording medium (approximately several hundred degrees Celsius) and reducing its coercivity. In this way, recording of a high-coercivity recording medium for which recording has been difficult with the conventional magnetic recording head due to a lack of recording field strength can be facilitated. For reproduction, a magnetoresistive effect element that is used in conventional magnetic recording is used.
In the thermally assisted magnetic recording system, laser light for heating the medium is guided to the recording head. As a laser light source, a small-size and small-power-consumption semiconductor laser diode is used due to the need for use within the magnetic disk apparatus package.
On the other hand, the energy assisted recording that employs a high frequency magnetic field as the energy is referred to as “high frequency magnetic field assisted magnetic recording” or “microwave assisted magnetic recording”. The recording medium is irradiated with a high frequency magnetic field separately from the recording field to make the magnetization of the recording medium resonate and easier to move, thus facilitating the recording of the high-coercivity recording medium for which recording has been difficult due to the lack of recording field strength. For reading, a magnetoresistive effect element that is used in conventional magnetic recording is used, as in thermally assisted recording.
In the high frequency magnetic field assisted magnetic recording, an element that generates the high frequency magnetic field is disposed in the vicinity of the recording magnetic pole. This element is referred to as a spin torque oscillator (STO). The STO is disposed between a main magnetic pole and a trailing shield. A high frequency magnetic field assisted magnetic recording head in which the STO is disposed in the vicinity of the recording magnetic pole is disclosed in Non-patent Document 1, for example. The STO has a magnetic-film stacked structure similar to a read sensor for GMR or TMR used in the head of a magnetic disk apparatus, and has the feature that it can be easily integrally formed with a conventional magnetic head.